The present inventors have previously invented a process for preparing a polymer composition having a property of releasing a physiologically active substance at a controlled rate which comprises contacting a polymerizable monomer and the physiologically active substance and irradiating them with light or an ionizing radiation to polymerize the monomer. (Japanese Patent Application No. 27,109/78, U.S. Ser. No. 18,617) and, further, on the basis of this invention, have accomplished a series of inventions of a process for preparing a polymer composition having the same property which comprises dropping or injecting a mixture of one or more monomers vitrificable at low temperatures containing a high molecular weight substance and the physiologically active substance into a medium to make the mixture into a shape of spherical structure and irradiating it with light or an ionizing radiation (Japanese Patent Application No. 51,239/78, U.S. Ser. No. 18,617). The inventors have also invented a process for preparing a polymer composition in which the elution rate of the physiologically active substance is controlled by pH which comprises irradiating a uniform mixture of a polymer soluble in a pH within a certain range, a polymerizable monomer and the physiologically active substance with light or an ionizing radiation to polymerize the monomer (Japanese Patent Application No. 105,306/78, U.S. Ser. No. 18,617), a process for preparing a polymer composition having the same property which comprises mixing a polymerizable monomer and a physiologically active substance in the presence or absence of a crystallizable substance, adding an adsorbent thereto and irradiating it with light or an ionizing radiation (Japanese Patent Application No. 106,097/78, U.S. Ser. No. 18,617), and a process for preparing a polymer composition containing an antitumor agent and having the property of releasing it at a controlled rate which comprises mixing a polymerizable monomer with two or more antitumor agents, or one or more antitumor agents and a substance promoting an antitumor effect and irradiating the mixture with light or an ionizing radiation (Japanese Patent Application No. 146,411/78, U.S. Ser. No. 95,496).
However, in the case of where two or more kinds of an antitumor agent are contained in a single matrix for simultaneously and eluting them (Japanese Patent Application No. 146,411/78, U.S. Ser. No. 95,496), in general, for example as shown in FIG. 1, the elution of each antitumor agent takes place simultaneously although it varies somewhat with the kind of antitumor agent.
Thus, simply from containing an antitumor agent in a matrix, the elution thereof reaches the saturation point at a certain period and it comes to be of no use as a controlled release agent. This tendency is not limited to the antitumor agent but is general for all physiologically active substances. And also in the case of mixing an adsorbent, a physiologically active substance and a polymerizable vinyl monomer simultaneously, and after dispersion subjecting them to radiation induced polymerization to prepare a controlled release matrix (Japanese Patent Application No. 106097/78, U.S. Ser. No. 18,617), it does nothing but making it possible to prolong the controlled releasing time and the profile of the releasing curve for the physiologically active substance is in agreement with FIG. 1.